Data capturing systems such as video security systems utilize video cameras to generate video signals representative of locations for which security surveillance is desired. In a typical system, some or all of the video signals are displayed on video screens for monitoring by security personnel. Some or all of the video signals are recorded on videotape, either to provide evidentiary support for the observations of security personnel or in cases where “real-time” human monitoring of the signals is impractical or is not desired.
However, videotape suffers from serious drawbacks as a storage medium, particularly in view of the large quantity of video information generated by video security systems. A major concern is the sheer quantity of tapes to be stored, especially when it is desired to record signals generated by a large number of surveillance cameras. Moreover, in a large system many videotape recorders may be required, resulting in a large capital expenditure, and also the need to allocate space for the recorders. Another problem is the need to frequently change tape cassettes.
Retrieving information of interest from recorded tapes presents additional challenges. It is the nature of video surveillance that a large part of the tape-recorded video surveillance signal is of no interest whatsoever, since it typically represents a static image of a hall-way or the like. Finding a particular sequence representing a significant event can be extremely difficult and time-consuming, requiring tedious human review of hours or days of tape-recorded signals.
There have been a number of attempts to overcome these disadvantages, but so far with limited success, or at the cost of additional drawbacks. For example, it is known to use “quad multiplexers” to combine signals from four video cameras into a single dynamic image, having four quadrants each dedicated to a respective one of the cameras. The resultant space-multiplexed signal can then be recorded, realizing a four-to-one compression ratio in terms of required storage medium. However, the multiplexed image suffers from a corresponding loss of spatial resolution, which may impair the value of the recorded images as evidence or may interfere with subsequent review. Also, the recording of multiplexed images does not address the problems involved in finding sequences of interest on the recorded tapes.
It is also known to record the surveillance video signals selectively in response to input from a human operator who is monitoring the signals or in response to signals generated by sensor devices arranged to detect events such as opening of doors or windows. This technique reduces the total information to be recorded, while preventing storage of much uninteresting information, but at the risk of failing to record significant events which cannot readily or timely be detected by sensors or human operators. Also, reliance on external input can result in unreliability and increased expense, particularly where human operators are to initiate recording.
Accordingly, what is needed is an apparatus that eliminates video cassette tapes and the related short comings thereof. The apparatus should be simple, cost effective and capable of being easily adapted to existing technology. The present invention addresses these needs.